Our major aim is to investigate pulmonary mechanics during high frequency oscillation (HFO). Mechanical factors are important because they can pre-determine many aspects of regional lung function. We propose to investigate the distribution and synchrony of regional lung filling, the stability of regional lung volume, and the pressure levels in alveolar spaces under the conditions of small tidal volume (1-250cc) high frequency (1-60Hz) oscillations. We will assess these factors by direct sampling of regional alveolar pressures in the excised canine lung. This will be accomplished using an alveolar capsule technique which samples regional alveolar pressure via pleural punctures. The alveolar capsule technique is ideally suited to assess these questions by virtue of its regional specificity. Data will be interpreted to discriminate between two non-linear mechanisms which are hypothesized to influence the factors above: a) preferential streaming of high velocity inspiratory flows along axial pathways, and b) regional expiratory flow limitation. These studies will facilitate development of strategies for clinical application of HFO which embody criteria for gas exchange, management of airspace pressure levels, and lung volume stability.